Systems and methods for displaying guidance images with spatial annotations during a guided medical procedure

ABSTRACT

The present disclosure provides systems and methods for generating spatial annotations within guidance images that are displayed during a guided medical procedure, where the spatial annotations provide spatial graduations indicating known length measures. The spatial measures may be employed to visually assess the sizes of anatomical and/or functional features displayed in the guidance images.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/279,412, titled “SYSTEMS AND METHODS FOR DISPLAYING GUIDANCE IMAGESWITH SPATIAL ANNOTATIONS DURING A GUIDED MEDICAL PROCEDURE” and filed onJan. 15, 2016, the entire contents of which is incorporated herein byreference.

BACKGROUND

The present disclosure relates to systems and methods that performtracking of medical instruments during a navigated medical procedure.

Pedicle screw implantation has become a relatively common procedure tosupport a number of degenerative or acute clinical conditions of thespine. A number of pre-planning software systems have been developed toaid the implantation of these screws, predominantly by allowing thesurgeon to size the width and length of screws that will be implantedduring the surgery. However, screw sizes determined prior to the surgeryare typically selected assuming ideal conditions such as optimal entrypoints and trajectory. If, during the surgery, these entry points andtrajectories are not exactly matched, the screw size selected prior tosurgery may not be optimal.

SUMMARY

The present disclosure provides systems and methods for generatingspatial annotations within guidance images that are displayed during aguided medical procedure, where the spatial annotations provide spatialgraduations indicating known length measures. The spatial measures maybe employed to visually assess the sizes of anatomical and/or functionalfeatures displayed in the guidance images.

Accordingly, in a first aspect, there is provided a method of performingtracking and navigation during a medical procedure, the methodcomprising:

detecting, with a tracking system, signals from one or more fiducialmarkers associated with a medical instrument, the medical instrumentcomprising an elongate portion characterized by a longitudinal axis;

processing the signals to determine a position and an orientation of themedical instrument;

employing a coordinate transformation to represent pre-operative imagedata and the position and orientation of the medical instrument within acommon reference frame; and

generating and displaying navigation images comprising:

-   -   a virtual representation of the medical instrument;    -   anatomical and/or functional features associated with the        pre-operative image data; and    -   a plurality of spatial annotations positioned at prescribed        locations along the longitudinal axis relative to the position        of the medical instrument,

wherein each spatial annotation identifies a respective image regionhaving a known length measure associated therewith, and wherein eachspatial annotation is configured such that the image region associatedtherewith is centered on the longitudinal axis and extends orthogonal tothe longitudinal axis;

each spatial annotation thereby enabling a visual assessment of the sizeof anatomical and/or functional features proximal to the longitudinalaxis.

In another aspect, there is provided a system for performing trackingand navigation during a medical procedure, the system comprising:

a tracking system for tracking the position and orientation of a medicalinstrument, the medical instrument comprising an elongate portioncharacterized by a longitudinal axis; and

computer hardware operatively connected to said tracking system, whereinsaid computer hardware is configured to:

-   -   employ a coordinate transformation to represent pre-operative        image data and the position and orientation of the medical        instrument within a common reference frame; and    -   generate and display navigation images comprising:        -   a virtual representation of the medical instrument;        -   anatomical and/or functional features associated with the            pre-operative image data; and        -   a plurality of spatial annotations positioned at prescribed            locations along the longitudinal axis relative to the            position of the medical instrument, wherein each spatial            annotation identifies a respective image region having a            known length measure associated therewith, and wherein each            spatial annotation is configured such that the image region            associated therewith is centered on the longitudinal axis            and extends orthogonal to the longitudinal axis;    -   each spatial annotation thereby enabling a visual assessment of        the size of anatomical and/or functional features proximal to        the longitudinal axis.

In another aspect, there is provided a method of performing tracking andnavigation during a medical procedure, the method comprising:

detecting, with a tracking system, signals from one or more fiducialmarkers associated with a medical instrument, the medical instrumentcomprising an elongate portion characterized by a longitudinal axis;

processing the signals to determine a position and an orientation of themedical instrument;

employing a coordinate transformation to represent pre-operative imagedata and the position and orientation of the medical instrument within acommon reference frame; and

generating and displaying navigation images comprising:

-   -   anatomical and/or functional features associated with the        pre-operative image data; and    -   a spatial annotation positioned at a discrete location along the        longitudinal axis relative to the position of the medical        instrument, wherein the spatial annotation identifies a        respective image region having a known length measure associated        therewith, and wherein the spatial annotation is configured such        that the image region associated therewith is centered on the        longitudinal axis and extends orthogonal to the longitudinal        axis;

the spatial annotation thereby enabling a visual assessment of the sizeof anatomical and/or functional features proximal to the longitudinalaxis.

In another aspect, there is provided a method of performing tracking andnavigation during a medical procedure, the method comprising:

detecting, with a tracking system, signals from one or more fiducialmarkers associated with a medical instrument, the medical instrumentcomprising an elongate portion characterized by a longitudinal axis;

processing the signals to determine a position and an orientation of themedical instrument;

employing a coordinate transformation to represent pre-operative imagedata and the position and orientation of the medical instrument within acommon reference frame; and

generating and displaying navigation images comprising:

-   -   anatomical and/or functional features associated with the        pre-operative image data; and    -   a plurality of spatial annotations positioned at prescribed        locations along the longitudinal axis relative to the position        of the medical instrument, wherein each spatial annotation        identifies a respective image region having a known length        measure associated therewith, and wherein each spatial        annotation is configured such that the image region associated        therewith is centered on the longitudinal axis and extends        orthogonal to the longitudinal axis;

each spatial annotation thereby enabling a visual assessment of the sizeof anatomical and/or functional features proximal to the longitudinalaxis.

In another aspect, there is provided a method of performing spatialannotations during a guided medical procedure, the method comprising:

generating and displaying navigation images comprising:

-   -   a virtual representation of a medical instrument tracked during        the medical procedure, the medical instrument comprising an        elongate portion characterized by a longitudinal axis;    -   anatomical and/or functional features associated with        pre-operative image data, wherein the pre-operative image data        and the position and orientation of the medical instrument are        known in a common reference frame; and    -   a plurality of spatial annotations positioned at prescribed        locations along the longitudinal axis relative to the position        of the medical instrument, wherein each spatial annotation        identifies a respective image region having a known length        measure associated therewith, and wherein each spatial        annotation is configured such that the image region associated        therewith is centered on the longitudinal axis and extends        orthogonal to the longitudinal axis;

each spatial annotation thereby enabling a visual assessment of the sizeof anatomical and/or functional features proximal to the longitudinalaxis.

A further understanding of the functional and advantageous aspects ofthe disclosure can be realized by reference to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the drawings, in which:

FIGS. 1A and 1B are screenshots of an example user interface thatdisplays two-dimensional guidance images having spatial annotationsindicating image regions having known length measures.

FIGS. 2A-2E illustrate examples of different types of spatialannotations that may be displayed.

FIG. 3 provides an example of a three-dimensional image having spatialannotations indicating image regions having known length measures.

FIG. 4 is a flow chart illustrating an example method of performingtracking and navigation during a medical procedure, in which guidanceimages are generated such that spatial annotations indicating imageregions having known length measures are displayed relative to thetracked position and orientation of a tracked medical instrument.

FIG. 5 is an example system for performing tracking and navigationduring a medical procedure.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described withreference to details discussed below. The following description anddrawings are illustrative of the disclosure and are not to be construedas limiting the disclosure. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentdisclosure. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present disclosure.

As used herein, the terms “comprises” and “comprising” are to beconstrued as being inclusive and open ended, and not exclusive.Specifically, when used in the specification and claims, the terms“comprises” and “comprising” and variations thereof mean the specifiedfeatures, steps or components are included. These terms are not to beinterpreted to exclude the presence of other features, steps orcomponents.

As used herein, the term “exemplary” means “serving as an example,instance, or illustration,” and should not be construed as preferred oradvantageous over other configurations disclosed herein.

As used herein, the terms “about” and “approximately” are meant to covervariations that may exist in the upper and lower limits of the ranges ofvalues, such as variations in properties, parameters, and dimensions.Unless otherwise specified, the terms “about” and “approximately” meanplus or minus 25 percent or less.

It is to be understood that unless otherwise specified, any specifiedrange or group is as a shorthand way of referring to each and everymember of a range or group individually, as well as each and everypossible sub-range or sub-group encompassed therein and similarly withrespect to any sub-ranges or sub-groups therein. Unless otherwisespecified, the present disclosure relates to and explicitly incorporateseach and every specific member and combination of sub-ranges orsub-groups.

As used herein, the term “on the order of”, when used in conjunctionwith a quantity or parameter, refers to a range spanning approximatelyone tenth to ten times the stated quantity or parameter.

Various example embodiments of the present disclosure provide systemsand methods for generating and displaying spatial annotations inguidance images that are displayed during a guided medical procedure,where the spatial annotations provide spatial graduations indicatingknown length measures. Such spatial measures may then be employed tovisually assess the sizes of anatomical and/or functional featuresdisplayed in the guidance images.

According to various example embodiments, the spatial annotations aredisplayed relative to the position and orientation of a medicalinstrument that is intraoperatively tracked during a medical procedure,such that the locations of the spatial annotations within the guidanceimages vary dynamically with the position and orientation of the trackedmedical instrument. The tracked medical instrument then may be employedas a dynamic ruler as it is moved relative to the anatomy of thesubject.

In some embodiments, the tracked medical instrument has an elongateportion (e.g. a shaft, handle, or other elongate feature) that ischaracterized by a longitudinal axis. The spatial annotations may thenbe displayed along the longitudinal axis of the medical probe, such thatthe spatial annotations provide dynamic graduations that “move” relativeto anatomical and/or functional features shown in the navigation imageas the medical instrument is moved relative to (e.g. toward, into,within) the tissue of the subject.

Referring now to FIG. 1A, an example of a guidance user interface isshown, where the a set of guidance images 102, 104 and 106 are generatedto provide spatial guidance during a medical procedure involving amedical instrument having elongate portion that is characterized by alongitudinal axis 100. The medical procedure of the present non-limitingexample involves the insertion of a pedicle screw through the pedicleshown at 125, and the guidance images 102, 104 and 106 show the positionand orientation of a pedicle probe 130, as tracked by a tracking system(this portion of the medical procedure occurs prior to the insertion ofthe pedicle screw).

In the present example illustrate in FIG. 1A, the guidance image 102shows a two-dimensional cross-section through the spinal column 120,where the two-dimensional image includes, and shows, the longitudinalaxis 100 of the medical instrument, as per the typical reslicing ofDICOM image data along the longitudinal axis. A plurality of spatialannotations 110 are generated along the longitudinal axis 100 of themedical probe, where each spatial annotation is centered on thelongitudinal axis 100. In the present example embodiment, the spatialannotations 110 are generated such that the image region (linearsegment) associated with each spatial annotation extends relative to thelongitudinal axis 100 in a direction that is perpendicular to thelongitudinal axis.

Each spatial annotation delineates (indicates) an image region (in thiscase, a linear image segment) that has a known length measure associatedtherewith. Each spatial annotation thus provides a graduation thatenables the operator/user to obtain a visual measure of the relativesize of anatomical and/or functional features in the guidance images.

The anatomical features may be, for example, various tissue structuresthat are pre-operatively (or intra-operatively) imaged according to awide variety of imaging modalities. Examples of functional featuresinclude, but are not limited to, activation maps obtained duringpre-operative functional magnetic resonance imaging, and diffusion mapsobtained during pre-operative diffusion-weighted magnetic resonanceimaging, real-time ultrasound which may include functional blood flow(Color/Power Doppler) imaging and/or shear wave imaging.

In some example implementations, as shown in FIG. 1 , two or moregraduations 105 may be displayed along the longitudinal axis, in orderto enable measurements of distances along the longitudinal axis. Thegraduations 105 may be fixed relative to the position and orientation ofthe medical instrument 130, such that they follow the medical instrument130 as the medical instrument is moved relative to anatomical and/orfunctional features shown in the guidance images.

The length measures associated with the spatial annotations may bedisplayed in the guidance images. For example, the length measures maybe provided in a legend (see, for example, FIGS. 2A-2E). In anotherexample implementation, the length measures may be displayed adjacent totheir respective spatial annotations.

As noted above, the two-dimensional image shown in view 102 of FIG. 1Ais generated such that the longitudinal axis 100 of the medicalinstrument, as determined via dynamic tracking of the position of theorientation of the medical instrument, lies within the two-dimensionalimage. The inclusion of the longitudinal axis 100 within the guidanceimage ensures that the spatial annotations represent length measuresthat lie within the guidance image, such that that each length measurerepresents is not spatially distorted via projection. It is noted thatthe slicing of DICOM image data along the longitudinal axis will resultin the longitudinal axis being present in two of the orthogonal imageslices. However, it will be understood that in some implementations, thetwo-dimensional slice may not fully encompass the longitudinal axis,provided that the longitudinal axis lies with sufficient proximity tothe image region including the spatial annotations, such that thespatial annotations represent correct length measures within aprescribed tolerance upon projection onto the image plane, such as atolerance within ±1, within ±2, within ±5, or within another suitablevalue as per the clinical requirements. In such implementations, theguidance image may include a projection of the longitudinal axis and thespatial annotations, and the spatial annotations may optionally berepresented as having a spatial extent that compensates for theprojection error.

FIG. 1A illustrates an example embodiment in which the spatialannotations are spatially arranged along the longitudinal axis in anordered configuration with respect to the length of their respectiveknown length measures. Accordingly, in some embodiments, the spatialannotations may be displayed in an ordered configuration along thelongitudinal axis according to an increasing or decreasing size of therespective known length measures. In one example implementation, thespatial annotations are spatially ordered such that the spatialannotation having the largest known length measure is displayed nearestto a proximal end of the medical instrument (as shown in FIG. 1A).

In the example embodiment shown in FIG. 1A, the spatial annotations aredisplayed such that they reside along the elongate portion of themedical instrument 130. The spatial annotations may be displayed suchthat the distalmost spatial annotation is displayed adjacent to thedistal end of the medical instrument, as also shown in FIG. 1A.

These example embodiments (involving the display of the spatialannotations along the elongate portion of the medical instrument) may bebeneficial when the medical instrument is employed such that asubstantial portion (e.g. greater than 5%, 10%, 15%, 20%, or 25%) of theelongate portion of the medical instrument is inserted within the tissueduring the medical procedure. For example, as shown in FIG. 1A, thepedicle probe 130 has a distal region that is inserted within thepedicle region of a spinal level, and the display of the spatialannotations along the elongate portion of the pedicle probe causes thespatial annotations to pass through the pedicle as the pedicle probe isinserted, along its longitudinal axis. The operator or user (e.g. asurgeon) observing the guidance images may therefore determine a measureor estimate of the pedicle width by watching the various spatialannotations pass through the pedicle region as the pedicle probe isinserted, and identifying the spatial annotation that best approximatesthe pedicle width (e.g. passes closest to the minimum observable widthof the pedicle). The passage of the spatial annotations through thepedicle region may also be beneficial in allowing an operator to observeany deviations of the pedicle probe from a central axis passing throughthe center of the pedicle.

The example embodiment illustrated in FIG. 1A may additionally oralternatively be employed by an operator to select a suitable pediclescrew for use during the medical procedure. For example, in some cases,a pedicle screw that is to be employed in a surgical procedure may beavailable in a plurality of sizes, and at least a subset of the spatialannotations may be displayed such that their respective known lengthmeasures correspond to standard screw diameters. In such an embodiment,an operator may select a suitable standard screw size by identifying thespatial annotation that has a desired diameter relative to the width ofthe pedicle. Accordingly, in general, in some embodiments, at least asubset of spatial annotations are selected such that their respectiveknown length measures corresponding to standard diameters of a tool(e.g. a fastener; where the tool is other than the medical instrument)that is employed during a medical procedure. In some exampleimplementations, a tool such as a pedicle screw may be configured to beexpandable to a user-controlled diameter, and the example embodimentsdisclosed herein may be employed for the determination of a suitableouter diameter when expanding the tool.

In another example embodiment, a subset of spatial annotations may bedisplayed such that they reside along the elongate portion of themedical instrument 130, while a remainder of the spatial annotations maybe displayed in a region along the longitudinal axis that lies beyond(distalward to) the distal end of the medical probe.

In yet another example embodiment, all of the spatial annotations may bedisplayed such that they are displayed in a region along thelongitudinal axis that lies beyond (distalward to) the distal end of themedical probe. An example of such an embodiment is shown in FIG. 1B,which shows a guidance user interface including a set of guidance images102, 104 and 106, in which the medical instrument displayed in theguidance images is an awl 135. In the example case of a spinal procedureinvolving the placement of a pedicle screw, the awl 135 is employedduring an initial portion of the procedure in order to select an entrypoint create an initial path within the cortical region of the bone.Since the awl 135 is only used for entering the cortical bone region,the awl does not penetrate deep into the tissue. Accordingly, in orderto generate spatial annotations that are suitable for the measurement orestimation of the pedicle width during the use of the awl 135, thespatial annotations 110 should be projected forward along thelongitudinal axis 100, as shown in FIG. 1B, such that the spatialannotations 110 lie in the pedicle region 125 that is distalwardrelative to the distal end of the awl 135.

Accordingly, in some example embodiments, the spatial annotations may bedisplayed such that they are projected forward in a distalward directionalong the longitudinal axis relative to the distal end of the medicalinstrument (e.g. distalward from the distal tip of an awl), such whenthe distal end of the medical instrument contacts an external tissuesurface (e.g. the outer surface of a bone) surface at a suitable entrypoint associated with the medical procedure, each spatial annotation isdisplayed proximal to a subregion of interest (e.g. overlapping ornearby to a central portion of the pedicle). The spatial offsets betweenthe distal end of the medical instrument and the spatial annotations maybe selected, for example, based on a reference atlas, optionallyaccording to the age and/or gender of the subject. Alternatively, thespatial offsets may be determined and configured based on pre-operativeimages of the subject.

In one example embodiment, the various spatial annotations associatedwith a medical instrument that is configured to contact external tissuewithout deeply penetrating the tissue (e.g. an awl, e.g. such that theportion of the elongate body of the medical instrument that penetratesthe tissue is less than 5%, less than 10%, less than 15%, less than 20%,or less than 25%) may be projected distalward relative to the distal endof the medical probe and arranged with a higher spatial density, alongthe longitudinal axis, relative to the density of the spatialannotations that are displayed for a medical instrument that isconfigured to substantially penetrate the tissue (e.g. such that theportion of the elongate body of the medical instrument that penetratesthe tissue is greater than 5%, 10%, 15%, 20%, or 25%). The higherdensity (along the longitudinal axis) of the spatial annotations thatare projected forward may be beneficial for clustering the spatialannotations nearby an anatomical and/or functional region of interestwhen the medical probe contacts the external tissue.

Although the example implementation shown in FIG. 1A involves thedisplay of a plurality of spatial annotations, in other exampleembodiments, a single spatial annotation may be shown. For example, asingle spatial annotation may be displayed at a discrete location alongthe longitudinal axis. In some example implementation in which thespatial annotation is employed to select the width of a tool that is tobe employed during a subsequent phase of the medical procedure, thespatial annotation may be displayed at a discrete location along thelongitudinal axis, such that an axial extent of the spatial annotation,along the longitudinal axis, is substantially less (e.g. less than 50%,less than 25%, less, than 20%, less than 15%, less than 10%, or lessthan 5%) than the axial length of the tool. This results in the displayof a spatial annotation that avoids occluding the guidance image, instark contrast to methods involving the rendering of a visualization ofthe tool that involve the display of the full spatial extent of thetool.

It is noted that although the two-dimensional images shown in thepreceding embodiments involve planar image slices, in other exampleimplementations involving two-dimensional guidance images, othergeometrical image configurations be rendered, such as two-dimensionalsurfaces having a cylindrical curvature, where the cylindrical surfaceis selected such that the longitudinal axis lies within the renderedtwo-dimensional image.

Referring now to FIG. 2A, an example guidance image is shownillustrating a specific example of a set of spatial annotations 110Athat are displayed along the longitudinal axis 100. The figure alsoshows a legend 115 that correlates each spatial annotation with itsrespective known length measure. Also shown in the figure are theoptional axial graduations 105 that enable length measurements along thelongitudinal axis 100. It is noted that the medical instrument is notshown in the guidance image, but in various clinical implementations ofthe methods and systems disclosed herein, it may be preferable todisplay a visual representation of the tracked medical instrument in theguidance image (e.g. as in FIGS. 1A and 1B). FIGS. 2B-2E illustrateadditional non-limiting examples of different types of spatialannotations (110B-110E) that may be employed to identify image regions.It will be understood that the example spatial annotations provided inFIGS. 2A-2E are merely illustrative in nature, and that a wide varietyof types and geometries of spatial annotations may be employed withoutdeparting from the intended scope of the present disclosure. Forexample, although the spatial annotations are shown according todifferent grayscale levels, the spatial annotations may be shown indifferent colours.

Although the examples embodiments that were described with reference toFIGS. 1A-1B and 2A-2E pertain to the display of two-dimensional images,it will be understood that the embodiments disclosed herein may beadapted to three-dimensional images, such as two-dimensionalrepresentations of three-dimensional images, virtual reality basedrenderings, and holographic images. In cases in which the navigationimage is configured to display a volumetric region, each spatialannotation may be generated to identify a spatial region surrounding thelongitudinal axis. For example, a spatial annotation may be generated asa circular shape surrounding the longitudinal axis, such as a ring or adisc (or one or more portions thereof). FIG. 3 illustrates an exampleimplementation of a three-dimensional navigation image that shows thepositioning of a pedicle probe 130 relative to the three-dimensionalsurface of the spinal region, where a set of ring-shaped spatialannotations 140 are distributed along the longitudinal axis of thepedicle probe. Additionally, to improve visibility of the annotationswhen the medical instrument is inserted into the tissue or when thedistalward projection lies within the 3D tissue volume it is possible toapply different transparency values to the 3D anatomical data.

Referring now to FIG. 4 , and flow chart is provided that illustrates anexample method of performing tracking and navigation during a medicalprocedure. In step 200, the position and orientation of the medicalinstrument (having an elongate portion characterized by a longitudinalaxis) are tracked. As noted above, this may be achieved using a trackingsystem that detects signals from one or more fiducial markers associatedwith (e.g. provided on or attached to) the medical instrument, and thedetected signals may be processed to determine the position andorientation of the medical instrument. A fiducial marker may be activeor passive, and may be detectable using an optical detector. An exampleoptical passive marker is a reflective sphere, or portion thereof, andan example active optical marker is an LED. Another example of a markeris a glyph, which may contain sufficient spatial and/or geometricalco-planar features for determining a three-dimensional position andorientation. For example, a glyph marker may include at least threecorner features, where the three corner features define a plane. In analternative example embodiment, the position and orientation of amedical instrument may be tracked via the detection of a surface profileof at least portion of the medical instrument, or structure attachedthereto.

In step 205, pre-operative image data, and the tracked position andorientation of the medical instrument, are expressed in a commonreference frame, such as an intra-operative reference frame (e.g. areference frame associated with a tracking system, or a reference frameassociated with the patient, such as a reference frame associated withstereotactic frame attached to the subject). This may be performed, forexample, by employing any suitable registration method involving theregistration of the pre-operative image data to an intraoperativereference frame. Example methods include the use of pre-operative andintraoperative fiducial markers, with optional intraoperativeidentification of the markers via a tracked instrument. Alternativemethods include the intraoperative detection of an anatomical surface(e.g. via structured light detection or other surface detectionmodalities) and the registration of the detected surface with a surfacedata obtained via the surface segmentation of pre-operative volumetricsurface data. Example image registration methods are described in U.S.Pat. No. 9,119,670, titled “SYSTEM AND METHODS FOR INTRAOPERATIVEGUIDANCE FEEDBACK”, filed on Oct. 31, 2012, which is incorporated hereinby reference in its entirety, and in International PCT PatentApplication No. PCT/CA2014/051120, titled “SYSTEM AND METHOD FORGENERATING PARTIAL SURFACE FROM VOLUMETRIC DATA FOR REGISTRATION TOSURFACE TOPOLOGY IMAGE DATA” and filed on Nov. 24, 2014, which isincorporated herein by reference in its entirety.

In steps 210 and 215 (which may be performed together as opposed toserially), a navigation image is generated including (i) a virtualrepresentation of the medical instrument, shown relative to anatomicaland/or functional features of the pre-operative image data, as per thetracked position and orientation of the medical instrument, and (ii) oneor more spatial annotations positioned at prescribed locations along thelongitudinal axis relative to the position of the medical instrument.Each spatial annotation identifies a respective image region having aknown length measure associated therewith. As illustrated in thepreceding example embodiments shown in FIGS. 1A-1B, 2A-2E and 3 , eachspatial annotation may be configured such that the image regionassociated therewith is centered on the longitudinal axis and extendsorthogonal to the longitudinal axis.

As shown in step 220, the annotated guidance image is then displayed(e.g. in a display window of a user interface), such that the spatialannotations enable a visual assessment of the size of anatomical and/orfunctional features proximal to the longitudinal axis of the medicalinstrument. As shown in the flow chart illustrating this example method,steps 200-210 may be repeated such that a series of navigation imagesare provided, thereby providing dynamic intraoperative tracking andnavigation with spatial annotations identifying known length measuresthat are spatially correlated with the tracked position and orientationof the medical instrument.

In some embodiments, the spatial annotations are displayed in eachguidance image (i.e. in each guidance image frame), at prescribedlocations along the longitudinal axis that are spatially fixed relativeto the tracked position and orientation of the medical instrument. Inother example embodiments, however, the annotations can be displayed ina more dynamic manner.

In one example implementation, the spatial annotations may be displayedwith temporal multiplexing, such that different spatial annotations areshown in different guidance images. For example, the guidance images maybe displayed such that the different spatial annotations are shown inseparate sequential displayed guidance images, and such that the fullset of spatial annotations are sequentially cycled as a function oftime.

In another example implementation, the positions of the spatialannotations along the longitudinal axis are varied as a function of timerelative to the position of the medical instrument, during the displayof the navigation images, such that the spatial annotations areperiodically translated along the longitudinal axis when the medicalinstrument is detected to be at rest, or approximately at rest; e.g.when a position of the medical instrument (e.g. the position of thedistal end of the medical instrument) is maintained within a prescribedspatial threshold (e.g. within ±1 mm, within ±2 mm, within ±3 mm, within±4 mm, within ±5 mm) within a prescribed amount of time (e.g. within 1second, within 2 seconds, within 3 seconds, within 4 seconds, or within5 seconds).

In some example implementations, the spatial annotations may bedisplayed according to the detected speed of motion of the medicalinstrument, such that navigation images including the spatialannotations are displayed only when the speed of the medical instrumentis determined to be below a pre-selected threshold. In another exampleimplementation, the navigation images including the spatial annotationsmay be generated and displayed with an increased magnification when thespeed of the medical instrument is below a pre-selected threshold. Theseexample embodiments may also be implemented according to whether or notthe medical instrument is detected to be at rest, or approximately atrest.

In another example implementation, the spatial annotations may bedisplayed such that a single spatial annotation is displayed at anygiven time, and where the display of a given spatial annotation isselectable via input from an operator. The input may be associated withthe rotational orientation of the medical instrument relative to thelongitudinal axis, such that as the medical instrument is rotated, thedifferent spatial annotations are selectively displayed. In one exampleimplementation, the user input may be employed to vary the known lengthmeasure associated with a spatial given annotation. For example, thelength measure associated with a given spatial annotation may be variedby rotating the medical instrument about its longitudinal axis whilemaintaining a position of the medical instrument (e.g. the position ofthe distal end of the medical instrument) within a prescribed spatialthreshold (e.g. within ±1 mm, within ±2 mm, within ±3 mm, within ±4 mm,or within ±5 mm).

In some example embodiments, the display of the spatial annotations maybe controlled based on operator input. For example, the spatialannotations may displayed only when the a position of the medicalinstrument (e.g. the position of the distal end of the medicalinstrument) is maintained at rest or approximately at rest, e.g. withina prescribed spatial threshold (e.g. within ±1 mm, within ±2 mm, within±3 mm, within ±4 mm, within ±5 mm) within a prescribed amount of time(e.g. within 1 second, within 2 seconds, within 3 seconds, within 4seconds, or within 5 seconds). In other example implementations, thedisplay of the spatial annotations may be toggled based on inputreceived from an input device such as a foot pedal, a touch-sensitivedisplay, input received by a mouse, keyboard or other physical inputdevice, voice commands received through a microphone, and gesture inputdetected, for example, via recorded images, or via input received by aproximity sensor embedded in the system. In some exampleimplementations, the spatial annotations may be displayed for aprescribed time interval, such as 1 second, 2 seconds, 3 seconds, 4seconds, or 5 seconds, after receiving input triggering the display ofthe spatial annotations.

It will be understood that the preceding example embodiments involvingsurgical procedures of the spine are merely provided as illustrativeexamples, and that various embodiments described herein may be employedand adapted to a wide variety of medical procedures. For example, inminimally invasive spine and/or cranial surgery tube retractors are usedto facilitate access to the target anatomy by gradually increasing thetube size. By tracking one or more of the tubes and showing associatedspatial annotations determination of the tube sizes to be used next andoverall trajectory can be made. In another example, during a biopsyprocedure of a tumor typically the viable rim of the tumor is targeted.When selecting an entry point with a tracked probe or biopsy needle onthe surface of the patient distalward spatial annotations shown near thetumor enable the surgeon to shift the entry point by a known distance totarget the center of the viable rim.

FIG. 5 provides a block diagram illustrating an example implementationof a system for implementing the example embodiments described above.The tracking system 365 is employed to track the position andorientation of one or more medical instruments 375, as described above.The medical instrument 375 is shown having fiducial markers 380 attachedthereto, and passive or active signals emitted from the fiducial markers380 are detected by the tracking system 365 (e.g. a stereographictracking system employing two tracking cameras). In an alternativeexample embodiment, the position and orientation of a medical instrumentmay be tracked via a surface profile detection system, such as astructure light detection system, that is employed to detect the surfaceprofile of a of at least portion of the medical instrument, or structureattached thereto, and to determine the position and orientation of themedical instrument via comparison of the detected surface profile with aknown surface profile.

FIG. 4 provides an example implementation of control and processinghardware 300, which includes one or more processors 310 (for example, aCPU/microprocessor), bus 305, memory 315, which may include randomaccess memory (RAM) and/or read only memory (ROM), a data acquisitioninterface 320, a display 325, external storage 330, one morecommunications interfaces 335, a power supply 340, and one or moreinput/output devices and/or interfaces 345 (e.g. a speaker, a user inputdevice, such as a keyboard, a keypad, a mouse, a position trackedstylus, a position tracked probe, a foot switch, and/or a microphone forcapturing speech commands).

Control and processing hardware 300 may be programmed with programs,subroutines, applications or modules 350, which include executableinstructions, which when executed by the one or more processors 310,causes the system to perform one or more methods described in thepresent disclosure. Such instructions may be stored, for example, inmemory 315 and/or other internal storage. In particular, in the exampleembodiment shown, registration module 355 includes executableinstructions for registering pre-operative image data 370 to anintraoperative reference frame, for example, according to one of theregistration methods described above. Guidance user interface module 360includes executable instructions for displaying a user interfaceaccording to the aforementioned methods, whereby spatial annotations,having reference length measurements associated therewith, aredynamically displayed with respect to the detected position andorientation of the medical instrument.

Although only one of each component is illustrated in FIG. 4 , anynumber of each component can be included in the control and processinghardware 300. For example, a computer typically contains a number ofdifferent data storage media. Furthermore, although bus 305 is depictedas a single connection between all of the components, it will beappreciated that the bus 305 may represent one or more circuits, devicesor communication channels which link two or more of the components. Forexample, in personal computers, bus 305 often includes or is amotherboard. Control and processing hardware 300 may include many moreor less components than those shown.

Control and processing hardware 300 may be implemented as one or morephysical devices that are coupled to processor 310 through one of morecommunications channels or interfaces. For example, control andprocessing hardware 300 can be implemented using application specificintegrated circuits (ASICs). Alternatively, control and processinghardware 300 can be implemented as a combination of hardware andsoftware, where the software is loaded into the processor from thememory or over a network connection.

A computer readable medium can be used to store software and data whichwhen executed by a data processing system causes the system to performvarious methods. The executable software and data can be stored invarious places including for example ROM, volatile RAM, non-volatilememory and/or cache. Portions of this software and/or data can be storedin any one of these storage devices. In general, a machine readablemedium includes any mechanism that provides (i.e., stores and/ortransmits) information in a form accessible by a machine (e.g., acomputer, network device, personal digital assistant, manufacturingtool, any device with a set of one or more processors, etc.).

Examples of computer-readable media include but are not limited torecordable and non-recordable type media such as volatile andnon-volatile memory devices, read only memory (ROM), random accessmemory (RAM), flash memory devices, floppy and other removable disks,magnetic disk storage media, optical storage media (e.g., compact discs(CDs), digital versatile disks (DVDs), etc.), among others. Theinstructions can be embodied in digital and analog communication linksfor electrical, optical, acoustical or other forms of propagatedsignals, such as carrier waves, infrared signals, digital signals, andthe like. As used herein, the phrases “computer readable material” and“computer readable storage medium” refer to all computer-readable media,except for a transitory propagating signal per se.

Some aspects of the present disclosure can be embodied, at least inpart, in software. That is, the techniques can be carried out in acomputer system or other data processing system in response to itsprocessor, such as a microprocessor, executing sequences of instructionscontained in a memory, such as ROM, volatile RAM, non-volatile memory,cache, magnetic and optical disks, or a remote storage device. Further,the instructions can be downloaded into a computing device over a datanetwork in a form of compiled and linked version. Alternatively, thelogic to perform the processes as discussed above could be implementedin additional computer and/or machine readable media, such as discretehardware components as large-scale integrated circuits (LSI's),application-specific integrated circuits (ASIC's), or firmware such aselectrically erasable programmable read-only memory (EEPROM's) andfield-programmable gate arrays (FPGAs).

The specific embodiments described above have been shown by way ofexample, and it should be understood that these embodiments may besusceptible to various modifications and alternative forms. It should befurther understood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover all modifications,equivalents, and alternatives falling within the spirit and scope ofthis disclosure.

The invention claimed is:
 1. A surgical navigation system comprising:computer hardware operatively connectable to a tracking system, saidcomputer hardware comprising at least one processor and memory, thememory comprising instructions executable by said at least one processorfor performing operations comprising: receiving, from the trackingsystem, signals from one or more fiducial markers associated with amedical instrument; processing the signals to determine a position andan orientation of the medical instrument; employing a coordinatetransformation to represent pre-operative image data and the positionand orientation of the medical instrument within a common frame ofreference; and generating and displaying a navigation user interfacecomprising: anatomical and/or functional features associated with thepre-operative image data; a plurality of virtual spatial annotationspositioned at prescribed locations along a longitudinal axis of themedical instrument relative to the position of the medical instrument,each virtual spatial annotation having a transverse spatial extentindicating a corresponding different absolute transverse length measure,the transverse spatial extent being determined in a direction orthogonalto the longitudinal axis; and numeric values of the different absolutetransverse length measures that correspond to the virtual spatialannotations, the virtual spatial annotations thereby enabling a visualrepresentation of the size of anatomical and/or functional featuresproximal to the longitudinal axis.
 2. The system according to claim 1further comprising the tracking system.
 3. The system according to claim1 wherein said computer hardware is configured to generate a virtualrepresentation of the medical instrument in the navigation userinterface.
 4. The system according to claim 1 wherein said computerhardware is configured such that at least a subset of the virtualspatial annotations are displayed at respective locations along anelongate portion of the medical instrument.
 5. The system according toclaim 1 wherein said computer hardware is configured such that at leasta subset of the virtual spatial annotations are displayed at respectivelocations that reside beyond a distal end of the medical instrument. 6.The system according to claim 5 wherein said computer hardware isconfigured such that the distance, along the longitudinal axis, betweeneach virtual spatial annotation and the distal end of the medicalinstrument, is selected such that when the distal end of the medicalinstrument contacts a bone surface at a suitable entry point associatedwith a medical procedure, each virtual spatial annotation is displayedproximal to a subregion of interest.
 7. The system according to claim 6wherein said computer hardware is configured such that the subregion ofinterest comprises a pedicle of a spine.
 8. The system according toclaim 7 wherein said computer hardware is configured such that eachabsolute transverse length measure represents a different tool diameter,thereby permitting the selection of a suitable tool diameter by visualcomparison of the virtual spatial annotations with the anatomical and/orfunctional features.
 9. The system according to claim 1 wherein saidcomputer hardware is configured such that at least two of the pluralityof virtual spatial annotations are spatially distributed along thelongitudinal axis.
 10. The system according to claim 9 wherein saidcomputer hardware is configured such that each virtual spatialannotation has a different spatial extent and represents a differentrespective absolute transverse length measure, and wherein the virtualspatial annotations that are spatially distributed along thelongitudinal axis are displayed along the longitudinal axis in anordered configuration according to an increasing or decreasing size ofthe respective absolute transverse length measures.
 11. The systemaccording to claim 10 wherein said computer hardware is configured suchthat the virtual spatially annotation having the largest absolutetransverse length measure is displayed nearest to a proximal end of themedical instrument.
 12. The system according to claim 1 wherein saidcomputer hardware is configured to generate and display a plurality ofnavigation images, each navigation image including the plurality ofvirtual spatial annotations, wherein the location of one or more virtualspatial annotations is varied as a function of time relative to theposition of the medical instrument during the display of the pluralityof navigation images.
 13. The system according to claim 1 wherein saidcomputer hardware is configured to perform the following operationsprior to generating and presenting the navigation user interfacecomprising the virtual spatial annotations: determining a speed of themedical instrument; comparing the speed of the medical instrument to apre-selected threshold; and determining that the speed of the medicalinstrument is below the pre-selected threshold.
 14. The system accordingto claim 1 wherein said computer hardware is further configured toperform operations comprising: determining a speed of the medicalinstrument; comparing the speed of the medical instrument to apre-selected threshold; and increasing a magnification of theannotations.
 15. The system according to claim 1 wherein said computerhardware is configured such that the navigation user interface includesa legend associating each virtual spatial annotation with its respectiveabsolute transverse length measure.
 16. The system according to claim 1wherein said computer hardware is configured such that the navigationuser interface comprises a visual representation of the longitudinalaxis.
 17. The system according to claim 16 wherein said computerhardware is configured to display a set of spatial graduations along thelongitudinal axis.
 18. The system according to claim 1 wherein saidcomputer hardware is configured such that the navigation user interfaceis a two-dimensional representation of a two-dimensional region, thetwo-dimensional region including the longitudinal axis.
 19. The systemaccording to claim 1 wherein said computer hardware is configured suchthat the navigation user interface is a two-dimensional representationof a three-dimensional region, the three-dimensional region includingthe longitudinal axis.
 20. The system according to claim 19 wherein saidcomputer hardware is configured such that the virtual spatialannotations have a circular shape.
 21. The system according to claim 1wherein said computer hardware is configured such that each virtualspatial annotation has a different spatial extent and represents adifferent respective absolute transverse length measure.
 22. The systemaccording to claim 1 wherein said computer hardware is configured toperform the following operations prior to generating and presenting thenavigation user interface comprising the virtual spatial annotations:determining a time duration over which the medical instrument resideswithin a pre-selected spatial range; comparing the time duration to apre-selected time window; and determining that the time duration isbelow the pre-selected time window.
 23. The system according to claim 1wherein said computer hardware is configured to perform operationscomprising: determining a time duration over which the medicalinstrument resides within a pre-selected spatial range; comparing thetime duration to a pre-selected time window; determining that the timeduration is below the pre-selected time window; and increasing amagnification of the annotations.
 24. A surgical navigation systemcomprising: computer hardware operatively connectable to a trackingsystem, said computer hardware comprising at least one processor andmemory, the memory comprising instructions executable by said at leastone processor for performing operations comprising: receiving, from thetracking system, signals from one or more fiducial markers associatedwith a medical instrument; processing the signals to determine aposition and an orientation of the medical instrument; employing acoordinate transformation to represent pre-operative image data and theposition and orientation of the medical instrument within a common frameof reference; and generating and displaying a navigation user interfacecomprising: anatomical and/or functional features associated with thepre-operative image data; a virtual spatial annotation positioned at aprescribed location along a longitudinal axis relative to the positionof the medical instrument, the virtual spatial annotation having atransverse spatial extent indicating a corresponding absolute transverselength measure, the transverse spatial extent being determined in adirection orthogonal to the longitudinal axis; and a numeric value ofthe absolute transverse length measure that corresponds to the virtualspatial annotation, the virtual spatial annotation thereby enabling avisual assessment of the size of anatomical and/or functional featuresproximal to the longitudinal axis.
 25. A non-transitorycomputer-readable storage medium having stored therein data representinginstructions executable by a processor for providing surgicalnavigation, the storage medium comprising instructions for performingoperations including: receiving, from a tracking system, signals fromone or more fiducial markers associated with a medical instrument;processing the signals to determine a position and an orientation of themedical instrument; employing a coordinate transformation to representpre-operative image data and the position and orientation of the medicalinstrument within a common frame of reference; and generating anddisplaying a navigation user interface comprising: anatomical and/orfunctional features associated with the pre-operative image data; aplurality of virtual spatial annotations positioned at prescribedlocations along a longitudinal axis of the medical instrument relativeto the position of the medical instrument, each virtual spatialannotation having a transverse spatial extent indicating a correspondingdifferent absolute transverse length measure, the transverse spatialextent being determined in a direction orthogonal to the longitudinalaxis; and numeric values of the different absolute transverse lengthmeasures that correspond to the spatial annotations, the virtual spatialannotations thereby enabling a visual representation of the size ofanatomical and/or functional features proximal to the longitudinal axis.26. A non-transitory computer-readable storage medium having storedtherein data representing instructions executable by a processor forproviding surgical navigation, the storage medium comprisinginstructions for performing operations including: receiving, from atracking system, signals from one or more fiducial markers associatedwith a medical instrument; processing the signals to determine aposition and an orientation of the medical instrument; employing acoordinate transformation to represent pre-operative image data and theposition and orientation of the medical instrument within a common frameof reference; and generating and displaying a navigation user interfacecomprising: anatomical and/or functional features associated with thepre-operative image data; a virtual spatial annotation positioned at aprescribed location along a longitudinal axis relative to the positionof the medical instrument, the virtual spatial annotation having atransverse spatial extent indicating a corresponding absolute transverselength measure, the transverse spatial extent being determined in adirection orthogonal to the longitudinal axis; and a numeric value ofthe absolute transverse length measure that corresponds to the virtualspatial annotation, the virtual spatial annotation thereby enabling avisual assessment of the size of anatomical and/or functional featuresproximal to the longitudinal axis.